add gtest header

Author: anutosh491

unittests/CppInterOp/DynamicLibraryManagerTest.cpp

@@ -6,6 +6,8 @@
 #include "llvm/Support/FileSystem.h"
 #include "llvm/Support/Path.h"
 
+#include "gtest/gtest.h"
+
 // This function isn't referenced outside its translation unit, but it
 // can't use the "static" keyword because its address is used for
 // GetMainExecutable (since some platforms don't support taking the